Resilient floor coverings are well known and are described for example in an article entitled "Flooring Materials" in Encyclopaedia of Polymer Science and Engineering, Wiley-Interscience, Volume 7 (1987), pages 233-247. Such floor coverings, as described in that article, are composite materials which comprise a transparent or translucent wear (upper) layer, often a decorative (intermediate) layer such as a printed patterned layer, and one or more backing (lower) layers. The composition of each layer in such composite laminate floor coverings is chosen to provide the desired balance of physical properties, both in that layer and in the whole composite laminate. Thus, for example, the properties of all the layers are desirably balanced so as to avoid curl.
The backing layer nearest the wear layer commonly contains one or more colored pigments and is commonly called the face ply. If no intermediate decorative layer is present, then the face ply itself provides the desired decorative appearance of the floor covering. If the floor covering includes a printed patterned layer, then the face ply serves to enhance the appearance of the printed patterned layer as seen through the wear layer. The face ply is often of a bright color, for example white, although it may be of a neutral color such as black. The other backing layers more remote from the wear layer commonly contain carbon black to provide a neutral opaque background behind the face ply. All the backing layers, including the face ply, commonly contain fillers such as calcium carbonate, hydrated aluminium oxide, kaolin or other suitable particulate or fibrous mineral fillers.
Films for incorporation in resilient floor coverings may be made by extrusion of suitable polymer compositions. For example, the backing layers including the face ply may be made by extrusion of polymer compositions based on ethylene/vinyl acetate or ethylene/alkyl acrylate, for example methyl or butyl acrylate, copolymers. It is often desirable to make differently-colored face plies at different times on a single extruder. Steps must therefore be taken to minimise the production of waste film at changeover. The extruder may be stopped, emptied and cleaned, but this is laborious and involves loss of production from the extruder whilst this is done. Alternatively, the color of the polymer composition fed to the extruder may be changed while the extruder continues to run, and waste film of intermediate color may be collected until the extruder has been flushed. This waste film can be shredded and used (with the addition of carbon black, if desired) for the manufacture of black backing layers. Nevertheless, this procedure requires additional operations to be carried out, and these operations may result in some degradation of properties of the thusly recycled polymer composition.
It is an object of the present invention to provide improved methods of manufacturing a film for incorporation as backing layer in resilient floor coverings, in particular a film which includes a face ply and to reduce loss of production when the color of a face ply is changed.